Connect one of the BNC test lead to Channel A of the oscilloscope. Connect the colored connector on the test lead to the LIN bus data signal terminal in the connector on the vehicle. This can normally be found on the vehicle wiring diagram. Connect the black test lead to battery negative or a good chassis ground. Once these are connected, start the Picoscope and observe the pattern.
As you can see from the example waveform, the LIN bus waveform is a square wave, representing the binary states in a serial data stream. The waveform observed should be free of obvious distortion and noise spikes, and the upper and lower levels should be approximately as in the example (for a 12 V system).
The lower level voltage (logic zero) should be less than 20% of battery voltage (typically 1 V) and the upper level voltage (logic one) should be more than 80% of battery voltage. Note that the voltage levels may change slightly when the engine is started.
We cannot decode the data stream using a scope, so the purpose of this test is to verify that the signal is both present and correct, and is not interrupted by moving the wiring harness or gently tugging the connectors. Faults may be specific to a particular function, such as a non-operating window, or general, where all the functions on the bus are not working. Before condemning a device, use the scope to check that it has power, ground, and a present and correct LIN signal.
Local Interconnect Network (LIN) bus communication is becoming more common on modern CAN Bus-equipped vehicles. It is essentially a low-speed, single-wire serial data bus (a sub-bus of the faster, more complex CAN Bus) used to control low-speed non-safety-critical housekeeping functions on the vehicle, especially windows, mirrors, locks, HVAC units, and electric seats.
The LIN bus is proving popular because of its low cost and also because it reduces the bus load of the supervising CAN network.
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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